The present invention relates to a novel system of hydrogen-gas generation and a method for generation of hydrogen gas by using the same in an industrially feasible scale.
As is well known, various industrial methods are practiced for the generation of hydrogen gas in an industrially feasible scale including the method of electrolysis of water, reaction of a metal with an acid, reaction of certain metals with a strongly alkaline compound, reaction of calcium hydride with water, steam reforming of methyl alcohol or methane in natural gas, releasing of hydrogen gas from a hydrogen-loaded hydrogen-absorbing metal or alloy, and so on. When a carborne hydrogen supply source is desired, however, these prior art hydrogen-generating means are each not suitable for the purpose of hydrogen supply to fuel cells which must naturally be very compact in size and light in weight. For example, some of these hydrogen-generating means can be operated only with consumption of a large quantity of energy. The yield of hydrogen gas is sometimes not high enough relative to the amount of the source material consumed. The efficiency of the process also cannot be high enough unless the apparatus or instrument therefor is quite large.
On the other hand, it is also known that hydrogen gas is evolved when a metal hydrogen complex compound such as lithium aluminum hydride LiAlH4 or sodium borohydride NaBH4, which is used as a hydrogenation reagent in laboratories, is brought into contact with water sometimes resulting in eventual hazardous explosion due to evolution of a large volume of hydrogen gas at a time requiring utmost care.
Thus, it is eagerly desired to develop a method and a source material for hydrogen gas generation by which the rate of hydrogen gas generation can be easily controlled with full safety.
The present invention accordingly has an object to provide a novel and improved efficient method for the generation of hydrogen gas and a system or agent therefor by which hydrogen gas can be generated efficiently in a high yield at a readily controllable rate without any danger of explosion.
Thus, the method of the present invention for the generation of hydrogen gas, which has been established as a result of the extensive investigations undertaken by the inventor with the above mentioned object, comprises the steps of:
(a) dissolving, in an aqueous alkaline medium, a metal hydrogen complex compound of a composition represented by the general formula
MIMIIIH4xe2x88x92nRn,xe2x80x83xe2x80x83(I)
or
MII(MIIIH4xe2x88x92nRn)2,xe2x80x83xe2x80x83(II)
xe2x80x83in which MI is an alkali metal, MII is an alkaline earth metal or zinc, MIII is an element selected from the group consisting of boron, aluminum and gallium, R is an alkoxy group, aryloxy group or acyloxy group and the subscript n is 0, 1, 2 or 3, to give a solution as a reaction medium; and
(b) contacting the reaction medium, with a fluorinated or unfluorinated metal or hydrogen-absorbing alloy having catalytic activity for the decomposition reaction of the metal hydrogen complex compound in the reaction medium.
Accordingly, the hydrogen-generating system of the invention comprises:
(A) an aqueous alkaline solution as a medium;
(B) a metal hydrogen complex compound of a composition represented by the general formula
MIMIIIH4xe2x88x92nRn,xe2x80x83xe2x80x83(I)
or
MII(MIIIH4xe2x88x92nRn)2,xe2x80x83xe2x80x83(II)
xe2x80x83in which each symbol has the same meaning as defined above, dissolved in the aqueous alkaline solution to form a reaction medium; and
(C) a fluorinated or unfluorinated metal or hydrogen-absorbing alloy having catalytic activity in contact with the reaction medium.